1. Field of the Invention
The present invention relates to a semiconductor device having a circuit which includes a thin film transistor (hereinafter referred to as a TFT), and a manufacturing method thereof. For example, the present invention relates to an electronic appliance in which an electro-optical device typified by a liquid crystal display panel or a light-emitting display device having an organic light-emitting element is mounted as a part thereof.
Applicants claim priority under 35 U.S.C. §119 to the following foreign application: Serial no. 2006-351985 filed Dec. 27, 2006 in Japan.
In this specification, the semiconductor device refers to all devices that can function by using semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and an electronic appliance are all included in the semiconductor device.
2. Description of the Related Art
In recent years, attention has been focused on a technique for forming a thin film transistor (TFT) using a semiconductor thin film (with a thickness of about several nm to several hundred nm) formed over a substrate having an insulating surface. The thin film transistor is widely applied to electronic devices such as an IC and an electro-optical device. In particular, the thin film transistor has been hurriedly developed as a switching element of an image display device.
In manufacturing of an electronic appliance having a semiconductor circuit, in order to improve efficiency for mass production, a mother glass substrate is used instead of a wafer substrate and a plurality of devices are often taken from one mother glass substrate. A mother glass substrate has a size of 300×400 mm for the first generation in the beginning of 1990, which has grown to 680×880 mm or 730×920 mm for the fourth generation in 2000. Production techniques have progressed, so that a plurality of devices, typically display panels, can be taken from one substrate.
Hereafter, in a film formation method using a spin coating method, the increase in size of a substrate will be disadvantageous in mass production because a mechanism for rotating a large substrate becomes large, and loss and waste amount of a material liquid increase. Further, when a film is formed by spin-coating a rectangular substrate, the film is likely to be formed unevenly and become circular with the center at a rotating axis. It is also difficult to adjust an apparatus used in a screen printing method to the increase in size of the substrate.
A droplet discharging technique typified by a piezo method or a thermal jet method, or a serial droplet discharging technique has attracted attention in recent years. This droplet discharging technique has been used in printing type and drawing an image; however, an attempt to apply the droplet discharging technique to a semiconductor field such as wiring pattern formation has begun in recent years. For example, a method for forming a wiring pattern by a droplet discharging technique is disclosed in Patent Document 1: Japanese Published Patent Application No. 2005-12179.